As the skilled person will be aware, VAR power refers to an imaginary component of the total power supplied by a power generation system, resulting from driving a reactive load such that the current and voltage are out of phase with one another. Driving an inductive load causes the current to lag the voltage, and vice versa for a capacitive load. Thus the reactive component of power can be compensated by adding capacitance/inductance as needed. The degree of reactive power is specified by the power factor cos φ where φ is the phase angle between the current and the voltage.
Examples of reactive power control systems can be found in, inter alia: US2010/246226; U.S. Pat. No. 7,142,997; US2004/164718; US2002/180408; U.S. Pat. Nos. 4,683,529; 4,545,997; 4,554,502; and U.S. Pat. No. 4,453,207.
New grid requirements are being imposed in regions where power generation from renewable sources, in particular solar, is becoming a larger proportion of total power generation. In particular these place requirements on VAR control for reactive power correction where differing sources supplying power to the grid could otherwise force the grid into an under-excited or over-excited mode during peak and off-peak cycles of the overall system. Thus, for example, the ability to absorb or export VLRs is required by new standards in Germany, in particular VDE4105, which will be mandatory for new products from January 2012. Thus the ability to react and correct and/or actively damp VARs is highly desirable.